This invention relates to the field of forming thin film electronic devices, and particularly to forming ternary semiconductor films having predetermined compositional gradients.
The technique of thin film deposition is an important process in the manufacture of solid state electronic devices. Many thin film devices are fabricated on compound semiconductor layers consisting of one or more regions having a uniform composition. Advances in the Molecular Beam Epitaxy (MBE) process have contributed to rapid progress in fabricating such devices. However, the growth and application of thin-films having a graded composition have received little attention. Although device modeling suggests many useful applications for graded composition devices, the difficulty of growing accurately graded structures having predetermined compositional profiles has severely restricted the development of such devices.
Graded structures have been grown using the MBE process by modulating the flux intensity of one of the molecular beams by varying shutter opening or by varying the effusive cell temperature. However, accurate and continuous control with fast response time is difficult. Many of the graded structures grown by the conventional MBE process have discrete compositional steps rather than smoothly varying profiles.
The use of the laser to radiate a single source of Hg.sub.0.7 Cd.sub.0.3 Te within a vacuum chamber has also been used to deposit thin films having the same composition as the target (J. T. Cheung, Appl. Phys. Lett 43(3), 255, Aug. 1, 1983). However, a method is needed for growing high quality, epitaxial films of Hg.sub.1-x Cd.sub.x Te having smoothly varying compositional gradients of any desired profile.